Ignition coil with permanent magnets in core



Sept. 28, 1965 M- BAERMANN 3,209,295

IGNITION COIL WITH PERMANENT MAGNETS IN CORE Filed March 20, 1964 -2Sheets-Sheet l INVENTOR. MAX BAffiMAA/A/ Lymw P 1965 M. BAERMANN3,209,295

IGNITION COIL WITH PERMANENT MAGNETS IN CORE Filed March 20, l964 2Sheets sheet 2 113 7151 Fig.4

p m y 122 w in 221 i D 115 I04 123 Fig. 5

INVENTOR. MAX BAL-W/VA/V/V United States Patent "ice IGNITION COIL WITHPERMANENT MAGNETS IN CORE Max Baermann, Benshergwulfshof, BezirkCologne, Germany Filed Mar. 20, 1964, Ser. No. 354,501 Claims priority,application Germany, Mar. 13, 1959, B 52,473 8 Claims. '(Cl. 336-155)This application is a continuationin-part application of my copendingapplication Serial No. 14,094, filed March 10, 1960, now abandoned.

The invention pertains to ignition coils for generating sparks forigniting combustible gas mixtures. Such ignition coils have found theirbest known use for gasoline motors in motor vehicles, but they can alsobe used for gas burners and oil heaters.

Most of the best known ignition coils are cylindrical and consist of alaminated core fitted with a high tension and low tension winding. Ahollow cylinder of laminated sheet metal is slipped over the low tensionwinding for better conduction of the magnetic field. The magnetic ironcircuit is not completely closed at the ignition coil, but has an airgap in order to enable a quick breakdown of the magnetic field. The timeof buildup of the magnetic field generated by the direct current isdetermined from the ratio of the electric resistance to the inductanceof the winding multiplied by a time constant. If such an ignition coilis used for the ignition of gasoline motors, then the time between twofirings is greater with a low r.p.m., while at high r.p.m.s the time isless, so that the magnetic field cannot completely build itself up asnecessary. At high speeds of rotation this results in the ignition sparklacking the power necessary for firing and the firing therefore misses.

French Reissue Patent No. 66,586 described an ignition coil in which thelaminations of the magnetic circuit consist of U-shaped, ferromagneticsheets made from Ferrocube material which has a low coercivity. The highand low tension windings are placed on one leg, while the other leg hasan air gap in which a permanent magnet of low permeability and highcoercivity is located. This permanent magnet is magnetized in thedirection of its smallest dimension, i.e., toward the ends of the legsforming the gap, and the magnet is so placed in the air gap that itsdirection of magnetization is opposite to the direction of the magneticfield generated by the low tension winding. The magnetic materialprovides an ignition coil improved over those used heretofore. However,it is not yet possible with this ignition coil to achieve the shortfiring times required by fast-running motors with the desired power inthe ignition spark.

The present invention contemplates an ignition coil which overcomes allof the objections heretofore known and others, and provides a coil whichis relatively small in physical size while still having the requiredpower output to supply the desired power of ignition spark at all motorspeeds.

In accordance with the present invention there is provided an ignitioncoil for generating electric sparks especially for firing of combustiblegas mixtures in internal combustion engines comprised of a closed loopof ferromagnetic material, a low coercivity, ferro-magnetic core havinghigh and low tension windings in overlapping relationship thereon, thecore extending across and within the loop with the ends of the corespaced from the inner sides of the loop, a pair of permanent magnets onewithin the space between each end of the core and the inside of theloop, the permanent magnets having a permeability 3,209,295 PatentedSept. 28, 1965 of approximately one and the permanent magnets being inmagnetic series with respect to each other.

In accordance with a further aspect of the present invention, the endsof the core facing the permanent magnets are fanned out to provide amagnet contacting area larger than the cross-sectional area of the corebody. By this construction, a large number of flux lines from themagnets can be funneled into the core for the purpose of saturating thesame as will be hereinafter described in detail.

Also in accordance with the invention, the core has a cross-sectionalarea such that it will be magnetically saturated by the magnetic fluxfrom the permanent magnets and will also be magnetically saturated bythe current flowing in the low tension or energizing coil around thecore.

Further in accordance with the invention, pole shoes preferably of twolayers, each of a plurality of ferromagnetic strips are placed betweenthe core ends and the permanent magnets with the strips of each layercrossing at right angles relative to the other layer to lessen eddycurrent loses at the ends of the core.

As a result of the invention, the high tension connection may be placedon a long side of the ignition coil, while the connections for the lowtension winding may be on the same or on the opposite side. Theconnections for the low tension winding can be developed as contactpins. This makes it possible to provide a simply and easily replaceableignition coil, in that a base plate may be provided on the motordistributor with two plug sockets to receive pins mounted in the base ofthe ignition coil.

As a further result of the invention, the high tension connection may beplaced on the top of the ignition coil, while the low tensionconnections are put on the same side. These ignition coils canadvantageously be set directly on the cover cap of the distributor.Special wiring connections are no longer necessary.

The principal object of the invention is the provision of a new andimproved ignition coil which is simple in constructon, small in physicalsize and yet which is capable of supplying a powerful ignition spark atall motor speeds.

Another object of the invention is the provision of a new and improvedignition coil wherein the parts of the coil may be so arranged thatimproved arrangements of the terminals may be obtained and inparticular, ignition coils may be obtained which can be plugged into andremoved from terminal sockets for ease of replacement.

A further object of the invention is the provision of a new and improvedignition coil wherein the coil around which the windings are placed whenthe windings are unenergized, is completely saturated by permanentmagnets having a high electrical resistance whereby when the low tensioncoil has been energized and is de-energized, a rapid reversal of theflux lines in the core will result.

The invention may take physical form in certain parts and arrangementsof parts, the preferred embodiments of which will be described in thisspecification and illustrated in the accompanying drawing which forms apart hereof and wherein:

FIGURE 1 is a side cross-sectional view of an ignition coil and its\associated energizing circuit illustrating a preferred embodiment of theinvention;

FIGURE 2 is an elevational perspective view of an ignition coil shown inFIGURE 1;

FIGURE 3 is a view somewhat similar to FIGURE 2, but showing a slightlyalternative construction;

FIGURE 4 is a cross-sectional view of an ignition coil illustratinganother form which the present invention may take; and,

FIGURE 5 is a side elevational view of the coil of FIGURE 4.

manent magnets.

Referring now to the drawings wherein the showings are for the purposesof illustrating preferred embodiments of the invention only and not forthe purposes of limiting same, FIGURE 1 shows an ignition coil as wellas the details to understand its operation. The ignition coil consistsof an elongated ferro-magnetic core 6, at whose ends permanent magnets 5and 7 are placed, having the magnetic polarity given in FIGURE 1, i.e.,in series. In accordance with the present invention these magnets areformed from a low permeability, high coercivity magnetic material suchas iron-barium-oxide and bismuth-manganese. Generally such magnets areformed by bonding small particles of iron-bari-um-oxide within a plasticbinder which may be rigid or flexible. The high coercivity of such amagnet, i.e., in the range of 1,600-2,400 oersteds or at least greaterthan 1,000 oersteds, makes it extremely 'diificult to demagnetize thepermanent magnets after they have been magnetized to saturation. The lowpermeability of these magnets, i.e. 1.02.0 and preferably nearer 1.0,enables these magnets to act as an air gap to the flow of magnetic fluxlines. These characteristics of the permanent magnets greatly improvethe electrical operation of an ignition coil if they are positioned inthe magnetic circuit of the coil as taught by this invention. A bondedmagnet of the type contemplated by the present invention has a highelectrical resistivity because the magnetic particles are separated bythe binder which is non-conductive. Accordingly, no substantial eddycurrents can flow in the magnets themselves. Such eddy currents in themagnets would tend to impede the flux change in the magnets and, thus,slow the response of the core to a change in flux.

These permanent magnets 5, 7 lie directly against the inner surface ofthe sides 1, 3 of a rectangular ferromagnetic short circuit bodyconsisting of sides 1, 2, 3, 4. The high tension winding 8 is put on thecore, and the low tension winding 9 upon this. One end of the hightension winding leads over a wire 10 to a spark plug 11 (here onlysymbolically indicated), while the other end 13 of the high tensionwinding with one end of the low tension win-ding 9 is connected to thepositive pole of a battery 16 over the wire 15. The second end of thelow tension winding is carried to the contact 18 over the wire 12. Thiscontact 18 isactuated by a cam placed on the axle 20. When the contact18 is closed, a current flows from the battery 16 over the wire 12, thelow tension winding 9 and over the wires 14, back to the battery 16. Thewinding direction of the coil is so chosen that a magnetic field isgenerated by the direct current flowing in the coil, which field isopposed to the magnetic field generated by the permanent magnets 5, 7.If the contact 18 is opened by turning the cam 19, the direct current isinterrupted, the'field generated by it collapses, and is immediatelybuilt up in the opposite direction because of the arrangement of thepermanent magnets 5 and 7. This rapid change of flux induces a hightension in the high tension winding 8, which is suflicient to create anignition spark in the spark plug 11. The condenser 17 prevents theformation of a spark across the contacts 18 when they are opened.

FIGURE 2 show-s a perspective view of the ignition coil shown in FIGURE1 by the windings 28. As may be seen from this figure, the core 26 hasends which are fanned out to fit the shape of the permanent magnets and27 on the ends which are turned toward them. The

fanned out ends of core 26 enables the magnetic flux lines generated bymagnets 25, 27 to be funneled into the body of core 26. Thus, a largenumber of flux lines are directed through the core by the seriallyarranged magnets 25, 27 and the core is saturated by these flux lines inone magnetic direction determined by the polarity of the per- It is alsopossible instead of connecting the core through the permanent magnets 25and 27 to the sides 29 and 23 of the short circuit body, as shown inthis drawing, to provide an air gap at both ends of the iron core 26.

Preferably, and in accordance with the invention, in all of theembodiments described, the core, for example, core 6 in FIGURE 1, shouldhave a cross-sectional area such that, for the material employed in thecore, the core is magnetically saturated by the magnetic flux generatedby the permanent magnets in one direction. Also and preferably inaccordance with the invention, the core 6 will be saturated in theopposite direction by the magnetic flux generated by the current in thelow tension winding 9.

With the arrangement shown, it will be appreciated that the core 6 andits associated windings will have a minimum of inductance so that thetime required for the build up of magnetic flux in the core 6 as the lowtension coil 9 is magnetized will be a minimum. Furthermore, when thecoil 9 is de-energized, the flux of the permanent magnets causes a veryrapid decay of flux in the core 6 and a build up of the magnetic flux inthe opposite direction resulting in the generation of a pulse ofelectrical energy in the high tension winding 8 of the maximum possiblevoltage and energy content.

Attention must also be called to the fact that the dimensions of thepermanent magnets 25 and 27 are such that no de-magnetizing of thesepermanent magnets results from the magnetic field generated by directcurrent in the low tension winding. The high coercivity of these magnetsassures that they are not dc-magnetized when they are subjected tomagnetic flux in the direction opposite to their magnetization.Electrically non-conducting permanent magnets with a coercive force of H750 oe. should preferably be used. These magnets in accordance with theinvention should have a specific resistivity in excess of 1012 ohm mm.

and a permeability approaching unity, i.e. 1.0.

FIGURE 3 shows another development of the invention. The magnetic shortcircuit body 46 is cylindrical and preferably consists of a rolled stripof sheet metal. The axis of the core 42 is perpendicular to the cylinderaxis. The ends of the core 42 are rounded, and permanent magnets 41 and43 having the given magnetic polarity and fitted to the cylinder, areslipped between the core and the short circuit body. However, it may beadvantageous for manufacturing reasons as shown in dotted lines, topress the permanent magnetic bodies in cylindrical form, and tomagnetize them only on the arc adjacent the ends of core 42. Thewindings are only indicated by the coils 45 with the wires 44. It isalso possible to close the cylinder openings with covers, which however,must be electrically insulated from the short circuit body to preventeddy currents.

The core 42 can also be so placed that its axis coincides with thecylinder axis. In this case both bases of the cylinder can be closed byplates. With such an arrangement however, the development of eddycurrents must be prevented by slitting the cylinder and the two covers.

The core and the magnetic short circuit body should preferably be madein the known manner of a material preventing the formation of eddycurrents, for example, a laminated sheet metal.

FIGURE 4 shows an ignition coil according to the invention. The hightension winding 102 is placed on the laminated core 101, and the lowtension winding 103 placed upon this. At the ends of the core 101 arethe pole shoes consisting of two layers 104 and 105, each of which aremade of parallel ferro-magnetic strips in sideby-side relationship.Strips of one layer cross at a right angle relative to the strips of theother layer.

The strips of one layer are insulated from each other and from theadjacent layer. Eddy currents are thus held down and improved operationresults. Eddy currents could also be prevented by making each layer froma single plate having a slit therein extending to the center of theplate, the slits of the separate layers of course being spaced 180 fromeach other.

The permanent magnets 106 with the given magnetic polarity are placedbetween the part 105 with a ferromagnetic short circuit 107 which is inthe form of a rectangular loop surrounding the coil in a horizontalplane as viewed in FIGURE 4. This loop is opened at the top and bottomand is closed at the bottom by the insulating plate 109 and the baseplate 110 and at the top by an insulating plate 111 and a cover plate112. This base plate 110 and the cover plate 112 are held in place bythe flanged housing 108. The end 119 of the high tension winding 104 isfastened to a contact piece 118 mounted in plate 111. This contact pieceis connected with the contact nipple 117 which is connected by thespring 116 with the connection coupling 115 for a high tension cable. Aspark-over from the high tension to the low tension connections isprevented by the insulating bushing 123. The second end 122 of the hightension winding is fastened with the terminal 113, to which also an end121 of the low tension winding is carried. The other end 120 of the lowtension winding is fastened with the terminal screw 114. The corearrangement in accordance with the invention thus enables a verymeritorious terminal arrangement for an ignition coil.

FIGURE 5 shows another development of the invention. The pins 132 and133 are provided instead of the terminal screws 113 and 114. As anexample, the pin 132 is connected with the circuit 120 and the pin 133with the circuits 121 and 122. The angle guides 130 are placed on bothfaces of the ignition coil for fastening it to a base plate.

The invention is not limited to the examples shown, but can also be usedfor other developments in which high power with small construction isneeded.

Having thus described my invention, I claim:

1. In an ignition coil for generating electric sparks especially for thefiring of combustible gas mixtures in internal combustion enginescomprised of a closed loop of ferro-magnetic material, a low coercivity,ferro-magnetic core having high and low voltage windings in overlappingrelationship thereon, said core extending across and within said loopwith the ends of said core spaced from the inner sides of said loop, apair of permanent magnets within the space between said core ends andthe inside of said loop, said permanent magnets having a permeability ofapproximately one and said permanent magnets being in magnetic serieswith respect to each other.

2. The combination of claim 1 wherein the cross sec tional area of saidcore and the magnetic flux generated by said two permanent magnets issuch that said core is magnetically saturated in a first direction whenthere is no appreciable winding created flux in said core.

3. The combination of claim 2 wherein the cross sectional area of saidcore is such that it will be magnetically saturated in a seconddirection opposite from said first direction by the magnetic fluxgenerated by the current in the low voltage winding.

4. In an ignition coil for generating electric sparks especially for thefiring of combustible gas mixtures in internal combustion engines,comprised of a closed generally rectangular loop of ferro-magneticmaterial and having inwardly facing sides defining a coil core recess, alow coercivity, magnetically high permeable magnetic core having highand low voltage windings in overlapping relationship there-around, saidcore being located Within said recess with the ends of said core spacedfrom said sides, a pair of permanent magnets, one placed at each coreend between said core end and said side, said permanent magnets having alow permeability and a pair of pole shoes between said magnets and theends of said core, said pole shoes being comprised of two layers oflaminated ferro-magnetic material, said laminations of each layercrossing at right-angles to the laminations of the other layer.

5. An ignition coil for generating electric spark, especially for anignition circuit of an internal combustion engine comprised of a closedloop of ferro-magnetic material, a ferro-magnetic core having high andlow voltage windings thereon extending across and within said loop withthe ends of said core spaced from the inner sides of said loop, apermanent magnet having low permeability placed between each end of saidcore and the inner side of said loop, said permanent magnets generatinga permanent magnetic flux in said core sufiicient to substantiallysaturate said core, and said low voltage winding, when energized,generating magnetic flux in said core substantially larger than and inopposition to said permanent magnetic flux and connecting means on saidcore to connect said winding into said ignition circuit.

6. The ignition coil defined in claim 5 wherein a ferromagnetic eddycurrent preventing member is positioned between said magnets and eachend of said ferro-magnetic core, said member being comprised of twolayers of laminated ferro-magnetic material, said laminations of eachlayer crossing at right angles to the laminations of the other layer.

7. The ignition coil as defined in claim 5 wherein each of said coreends are provided with a pole shoe between said core and one of saidmagnets, said shoes adjacent said magnet having .a substantially greatercross-sectional area than said core.

8. In an ignition coil for generating electric sparks es pecially forthe firing of combustible gas mixtures in internal combustion enginescomprised of a closed loop of ferro-magnetic material, a low coercivity,ferro-magnetic core having high and low voltage windings in overlappingrelationship thereon, said core extending across and within said loopwith the ends of said core spaced from the inner sides of said loop, apair of permanent magnets within the space between said core ends andthe inside of said loop, said permanent magnets having a permeability inthe order of substantially 1.0, a coercivity greater than ap proximately1,000 oersteds and a high electrical resistivity.

References Cited by the Examiner UNITED STATES PATENTS 2,218,711 10/40Hubbard 336l10 X 2,699,530 1/55 Latimer 336 X 2,730,681 1/56 Went et al336'110 3,060,394 10/62 Maeda 336136 JOHN F. BURNS, Primary Examiner.

1. IN AN IGNITION COIL FOR GENERATING ELECTRIC SPARKS ESPECIALLY FOR THEFIRING OF COMBUSTIBLE GAS MIXTURES IN INTERNAL COMBUSTION ENGINESCOMPRISED OF A CLOSED LOOP OF FERRO-MAGNETIC MATERIAL, A LOW COERCIVITY,FERRO-MAGNETIC CORE HAVING HIGH AND LOW VOLTAGE WINDINGS IN OVERLAPPINGRELATIONSHIP THEREON, SAID CORE EXTENDING ACROSS AND WITHIN SAID LOOPWITH THE ENDS OF SAID CORE SPACED FROM THE INNER SIDES OF SAID LOOP, APAIR OF PERMANENT MAGNETS WITHIN THE SPACE BETWEEN SAID CORE ENDS ANDTHE INSIDE OF SAID LOOP, SAID PERMANENT MAGNETS HAVING A PERMEABILITY OFAPPROXIMATELY ONE AND SAID PERMANENT MAGNETS BEING MAGNETIC SERIES WITHRESPECT TO EACH OTHER.